The present invention relates to etching a layer having features of different aspect ratios. More specifically, the present invention relates to reducing microloading during the etching of an etch layer having both open and dense features.
During semiconductor wafer processing, sometimes a semiconductor device may have both open and dense features. The open features have wider widths, while the dense features have narrower widths. As a result, the semiconductor device may have features of different aspect ratios. The aspect ratio of a feature is the ratio between the height and the width of the feature. Thus, if the heights of all the features of a semiconductor device are approximately the same, then the open features have relatively low aspect ratios, while the dense features have relatively high aspect ratios.
During the etching of such semiconductor devices having features of different aspect ratios, and especially when the aspect ratios of the features are high, microloading is becoming a common problem. As a result, the open features etch faster than the dense features. Often, when the etching of the open features is completed, the etching of the dense features may only have been completed partially. This is known as “aspect ratio dependent etching.” Continuing the etch process in order to complete the etching of the dense features may cause the open features to be etched into the layer(s) beneath the layer being etched, such as the substrate, and damage the semiconductor devices.